Would you mind expanding on that a bit? It'd be great to know which advice helped the most and at what level of preexisting tools the project will actually be built.

A surprising number of customers want something written from scratch just so they own the code and don't have any licensing hassles. With works under the GPL or Artistic License, I find customers are usually okay with reusing them once the licenses are explained.

Other customers want things written from scratch because they don't want their competitors to be sold their business logic in the form of the software you develop for them. For this very reason my standard contract states that business logic and general utility code will be kept separate. Any existing utility modules remain the property of their current owners, of course. I retain the rights to improve and reuse any non-specific utility modules I bring in from my private repository or develop for the project and license it to the customer royalty free forever. Anything that has to do with the customer's actual business operations is a work for hire and I can't reuse it.

Some customers just don't know how customizable or even simply configurable existing software can be and assume they need something new.

It's nice to know what objections a customer raises for what reasons. It's even nicer to know how certain objections have been removed through communication.